This study will determine whether emergency medical technicians (EMTs) equipped with defibrillators can improve survival from out-of-hospital cardiac arrest. Outcomes of death, admission, discharge, and long-term survival as well as health status of survivors will be determined. The sequential implementation of emergency services in the study area will enable comparisons of outcomes between three levels of service (EMT, EMT/Defibrillator trained, and paramedic). Adjacent communities will serve as a paramedic control. The findings of this study will have importance in areas that cannot support full paramedic programs and may also suggest changes in the delivery of paramedic services. A second phase of study examines the effectiveness of EMT/Defibrillator-trained service when used in areas already served by paramedics.